The present invention relates to imaging devices, and, more particularly, to an image sensing device which receives incident light so as to three-dimensionally sense an object.
In conventional three-dimensional picture image processing, when an object is three-dimensionally sensed, a lens is moved forward or backward along the optical axis with respect to an imaging device. Thus, a plurality of planar images which are focused at different object focal points before and after a portion of interest of an object can be sequentially sensed by using a normal imaging device having one focal surface, such as a solid state imaging device. In this case, the lens used has a relatively small focal depth, so that a peripheral image portion, i.e., an image in a region other than a clearly focused image portion included in an image incident on a focal surface of the imaging device is greatly out of focus. Based on differences in a focused state, only a focused image portion is extracted from a sensed image.
When a lens is moved, a focal point in an object space is moved, and a focused image region in the sensed image is changed upon this movement. Therefore, if the lens is moved stepwise at a constant pitch, a plurality of focused images corresponding to object distances at equal intervals can be obtained. If image processing is performed so as to overlap these image data in accordance with the distance over which the lens is moved, three-dimensional image data of an object of interest can be reconstructed. It can be said that such recognition of three-dimensional image data is similar to that when three-dimensional topography of a mountain is captured by overlapping images, each representing the contour of the mountain along contour lines at equal intervals.
The above-mentioned three-dimensional image reconstruction technique applies to the case wherein a micro object which can be microscopically observed is to be three-dimensionally apprehended to a high degree of precision. This technique can also be applied to the eyes of an automatic assembly robot which can both automatically recognize objects conveyed by a belt line at various heights, and select a target object so as to mount predetermined parts thereon. In this case, according to the conventional three-dimensional image reconstruction technique, since the lens is generally moved so as to sequentially sense a plurality of images by a single image sensor, extra time is required to obtain a final three-dimensional image. Particularly when the conventional technique is applied to a microscopic image field, it is very difficult to move a lens at high speed because a bright, high-magnification lens is large and heavy. As a result, three-dimensional image processing speed is further degraded.
In order to overcome such a drawback, a plurality of optical paths can be provided so as to simultaneously sense a plurality of images by a single solid state imaging device. However, with this method, the arrangement of the imaging device as a whole becomes complex, and drive control for image reconstruction of the images sensed by the imaging device becomes extremely cumbersome, thus preventing practical application.